The method and apparatus of this invention are ones relating to the cutting of pattern pieces from sheet material by means of a cutting tool moved along lines of cut defining the pattern pieces and wherein as the cutting tool is moved along a line of cut defining a pattern piece the cutting of that pattern piece is interrupted, the cutting tool is removed from cutting engagement with the material, and the material is advanced to bring a fresh segment of It to the cutting station before the cutting of that pattern piece is resumed.
After pattern pieces are cut from sheet material they are removed either by hand or by machine from the adjacent waste material. To allow an efficient separation it is quite important that the pattern pieces be cleanly cut from the Waste material and that no uncut strings, threads or connecting bridges exist between the pieces and the waste material. If such uncut features exist the involved pattern pieces may fail to be removed or expensive time consuming additional manual steps may have to be performed to complete the separation. One way to eliminate or at least reduce this problem is to cut each pattern piece with a single complete movement of the cutting tool along the periphery of each pattern piece without removing it from start to finish from cutting engagement with the material. Such "all-at-once" cutting of a pattern piece is not, however, always practical or possible and it may in many instances be desirable or necessary to interrupt the cutting of a pattern piece periphery with the cutting tool being withdrawn from cutting engagement with the material during such interruption. Unfortunately, the points at which these interruptions occur tend to be points at which incomplete cutting of the pattern pieces from the waste material may occur. If the periphery of a pattern piece includes a sharp corner it is known, to avoid uncut threads and as described in U.S. Pat. No. 4,133,233, to cause the tool as it approaches the corner point to overcut, that is to cut beyond the corner point, before being withdrawn from the material, rotated and brought back to the corner point for further cutting along the peripheral line away from the corner point.
Until recently, conveyorized cutting machines have been designed with cutting station lengths long enough to make it practical, if desired, to cut most or all of the wanted pattern pieces so that each is cut in a single continuous cycle of the cutting tool around its periphery. Typically, the cutting stations of these machines have been 13 to 20 feet or more in length. Since the cost of such a machine is directly proportional to its cutting station length a machine with a shorter cutting station can offer advantages of lower cost and of requiring less floor space. A shortened cutting station, however, may make it difficult or impossible to design cutting markers permitting each pattern piece to he cut all at once without shifting the material relative to the cutting station. That is, as the cutting station length is shortened it becomes more necessary to cut some pattern pieces in two or more stages with the work material being advanced between each stage.
As the cutting tool is moved along a line of cut in cutting engagement with the material it exerts forces on the material tending to displace or distort it from its neutral condition. The principle one of these forces is usually a forwardly directed force parallel to the line of forward movement of the cutting tool relative to the material, but significant lateral forces are also sometimes involved, particularly when cutting curved lines. When the tool is withdrawn from cutting engagement with the material, the forces exerted by the tool on the material are removed and the material relaxes. When the tool is returned to cutting engagement with the material to continue cutting along the same line, if it is inserted at exactly the same point as its point of withdrawal, or other point of furthest advance if different from the point of withdrawal, the now relaxed material is likely to have a slightly different disposition on the supporting surface than when the tool first arrived at that point, so that some threads or portions of the material may remain uncut as the cutting tool moves forwardly along the cut.
If the cutting tool is a knife reciprocated along a cutting axis extending generally perpendicularly to the material being cut, such knife generally has a sharpened forward cutting edge, an unsharpened rear edge parallel to the forward edge and an inclined sharpened lower edge terminating in a lowermost point. The lowermost point may be either in line with the rear edge or in line with the sharpened forward edge depending on the direction of inclination of the sharpened lower edge. If the lowermost tip of the knife is in line with the rear edge the sharpened lower edge tends to generally face forwardly toward the uncut material as the knife is advanced forwardly along the line of cut. The force exerted on the material by the knife also tends to push the material forwardly. If the knife is withdrawn from the material the material tends to relax rearwardly. If the knife is now immediately returned to the material at the point of withdrawal the generally forwardly facing inclined lower edge of the knife will tend to engage and cleanly cut the rearwardly displaced material since the inclined lower edge pushes such material forwardly against the adjacent body of uncut material to achieve a good cutting action, assuming the knife has a sufficient width to extend over all of the rearwardly displaced material and penetrates into the material forming the supporting surface for the work material. On the other hand, if the lower point of the knife is in alignment with the forward cutting edge the inclined lower sharpened edge faces generally rearwardly relative to the line of cut. If this blade is removed and reinserted at the same point into the material during a cutting operation the portion of the material which relaxes rearwardly during the removal of the knife is, after re-insertion of the knife, engaged by the rearwardly facing lower inclined surface which tends to urge the material it engages rearwardly toward the already cut portion of the line. Therefore, there is no back-up material tending to resist rearward movement of the relaxed material with the result that such relaxed material may not be completely cut, particularly if the inclined lower edge of the knife is somewhat dull.
As mentioned, in the case of conveyor type cutting machines or the like, where the material is cut one lengthwise segment at a time, it is often impractical, particularly if the cutting station is of relatively short length, to arrange the pattern pieces in a cutting marker so as to have each pattern piece contained within one segment permitting its being cut in one continuous cycle of the cutting tool. Instead, it is often desirable or necessary that at least some of the pattern pieces have portions falling into two or more adjacent segments. This means that one part of such a pattern piece is cut while a first segment of the material is positioned at the cutting station, and the cutting of the pattern piece is then interrupted and continued at a later time when another part is cut while the next adjacent segment is positioned at the cutting station. The points at which the periphery of such a pattern piece intersect the dividing line between adjacent segments of the material ar points at which clean cutting problems are likely to occur due to relaxation or other shifting or repositioning of the material taking place at such a point between the time of first cutting at that point and the time of later cutting at the same point.
The general object of the invention is therefore to provide a method and apparatus for overcoming clean cutting problems of the type mentioned above arising from the cutting of a first portion of a pattern piece periphery at one time and the cutting of the remaining portion of said periphery at a later time with the cutting tool being removed from cutting engagement with the material and the material being advanced relative to the cutting station between the cutting of the two involved periphery portions.
Other objects and advantages of the invention will be apparent from the following detailed description of preferred embodiments of the invention and from the accompanying drawings and claims.